As for your code, I see that you call initTimers() and then immediately call pinMode(PWM_PIN, OUTPUT);. All the pins are already set to OUTPUT in the initTimers(), and I think that might be messing with your results. I only got the hi-res PWM to work when I called pinMode(pin, OUTPUT); on each pin before changing all the timer settings.
So I’d comment all pinModes out and check if that works.
@jvanier, thanks for sharing that information. Good to hear the Particle team is working on integrating this into the firmware.